meta.h: inherit from TrueType/FalseType where applicable

To reduce repetition and to provide a proper type hierarchy,
let type traits inherit from TrueType and FalseType.
Add a wrapper for constant string references
Add documentation to new string API
Doxyfile: expand internal RAPIDJSON_DISABLEIF_RETURN macro
update string API tests
GenericStringRef: disallow assignment, const string pointer
GenericValue: fixup bool constructor

With the new string handling API, the constructor taking a `bool`
parameter matches in some unwanted cases, as pointers can be casted
to `bool` implicitly.

Add a SFINAE helper to this constructor to avoid matching arbitrary
pointers.  To avoid confusion for the user, this mechanism is hidden
from the Doxygen documentation.
adopt AddMember tests from #47 (726f986,b7bf73c)
GenericValue: add Move()
tutorial.md: document GenericValue::Move()
tutorial.md: update for new string API
Merge pull request #57 from pah/cleanup/string-handling

Improved handling of (constant) strings
travis-doxygen.sh: avoid leaking the GitHub token in build log
Merge pull request #60 from pah/fix/travis-ghtoken

travis-doxygen.sh: avoid leaking the GitHub token in build log
Change travis token
Fixes travis token
Fixes whitespaces in travis script
Fixes #59 by adding bool return value for each event handler function
Fixed readertest compilation error
MSVC: fix SSE/intrinsic support

MSVC with enabled RAPIDJSON_SSE2/RAPIDJSON_SSE42 requires the explicit
definition of the `_BitScanForward` intrinsic.  This can be reliably
ensured by including "intrin.h" and properly marking '_BitScanForward'
as intrinsic.

Confirmed on MSVC 2005, 2008.
Should fix https://code.google.com/p/rapidjson/issues/detail?id=96